1. Field of the Invention
The present invention relates to multi-layer circuit boards and, particularly, to the inspection of such boards during their fabrication.
Multi-layer circuit boards have been defined as an interconnect package which contains more than two layers of circuitry. Having grown out of space and military applications in the early 60s, multi-layer boards are now used in many commercial applications. The various types of multi-layer boards fall into several categories, all sharing common problems, to varying degrees.
2. Description of the Prior Art
One problem encountered in the fabrication of multi-layer boards is dimensional stability, or the lack of it, as the individual layers are processed. That is, each layer is designed in anticipation of precise registration with the other layers that form the multi-layer board. However, unless each of the layers undergoes identical dimensional alterations during its individual processing, precision that existed in the original artwork may be lost. This could result in a critical misalignment in the multi-layer board and result in its rejection. In other instances, misregistration may be compensated for after lamination, and during drilling, by providing a compensating offset within the drilling operation.